The operation of equipment in remote and inaccessible locations is difficult and, at time, impossible since there is no information available as to the condition or the occurrence of an event in such remote location. A typical example of a remote and inaccessible location is a subsea marine wellhead. The operations in a subsea marine wellhead are numerous and difficult to determine by the operations on the drilling vessel whether or not the exact desired operation has been successful. Examples of the kinds of operations contemplated herein are the landing of a casing hanger on the housing seat, the proper setting of the annulus seal, the positioning of a tool or component at a particular level or orientation within the wellhead, the strain on a component within the wellhead as an indication of the completion of a downhole cold forging operation or merely the application of a preselected amount of torque or other load to a component within the wellhead.
Prior to the present invention, the operations contemplated herein were done from a drilling vessel at the surface of the water and either no indications or very limited indications have been available as to whether or not such operations have been successfully completed. The penalty for failure of completion of such operations successfully has been at least having to recover the string and other equipment to the surface and to redo the operation completely, usually with new equipment. Failure to complete some operations can result in damage to the wellhead and possible other damage to the well.
While well logging has for years been accomplished in well bores both on land in marine applications, the information was normally transmitted back to the surface electrically by direct wiring or recorded by the tool in the well bore and the tool recovered to the surface. The information which such devices have acquired is not helpful in providing the desired completion of operations information which is desired.
Some information has been provided from a well bore for directional drilling purposes but this information is generally an indication of the direction and inclination taken by the drilling tool during directional drilling operations. Such information did not provide any signal which would be sufficiently complete for any operations other than the controlling of the direction of the drilling.
There has been a considerable amount of work on systems and apparatus for use to make measurements while drilling. These measurements include transmitting information, such as logging data and transmitting to the surface on longitudinal and torque pulses in the drill string (U.S. Pat. Nos. 3,813,656 and 3,830,389; utilizing an acoustic signal transmitted through the drill string U.S. Pat. Nos. (3,900,827 and 4,066,995); generating mud pulses and transmitting through the drilling fluid (U.S. Pat. Nos. 3,958,217, 4,001,775, 4,134,100, 3,821,696, 3,949,354 and 3,982,224); sonic signals detect change in mud flow rate from drill string to annulus (U.S. Pat. No. 4,527,425); information electrically transmitted to the surface over wires (U.S. Pat. Nos. 3,825,078, 4,121,193 and 4,126,848); well logging information transmitted in the range from 1-30 Hertz and includes repeater stations (U.S. Pat. No. 4,087,781); and pressure pulses generated in the string and detected at the surface as stress changes in the material of the drill string wall (U.S. Pat. No. 4,066,995).
As can be seen from a review of such prior art references, none of them address the problem of providing information to the surface to indicate the position of equipment being used within a subsea wellhead in a marine well.